The present invention relates to an air-ventilating valve which functions to allow surrounding atmosphere to enter a conduit or pipeline, when the surrounding pressure exceeds the atmospheric pressure in the conduit by a predetermined amount, and to block the release of moist and warm air in relation to the surrounding atmosphere from the conduit to said surrounding atmosphere. The valve includes two coaxial and upstanding seat projections, each of which lies essentially in a common plane, and a vertically movable valve member which includes an annular sealing element. The sealing element bridges a throughflow gap between said projections when the valve is closed and lies sealingly against respective sealing projections. The valve member is arranged to move to a valve closed position under the influence of gravity.
Air-ventilating valves of the kind concerned are well known and find use, e.g., in the upper end of waste pipes or soil pipes, primarily to prevent odors from escaping via the upper end of the soil pipe or waste pipe. In this regard, the upper end of the soil pipe (and the ventilating valve) can be positioned inwardly of the outer roof of the building concerned, for example in the attic or loft, so as to obviate the need of providing a pipe lead-through to the outside of the roof. The ventilating valve is also constructed to allow air to enter the pipe when the need arises, for instance as a result of a subpressure generated in the pipe after having flushed a water closet connected thereto.
It will be understood, however, that ventilation valves of the kind concerned find use in many other situations in which there is an interest in preventing the departure of gas from a pipeline or conduit and where it is necessary, at the same time, to be able to allow gas to enter the conduit when the level of pressure therein falls beneath the pressure of the ambient atmosphere to a given extent.
To ensure the greatest possible reliability of the valve in operation, the valve is normally constructed so that the valve member will move to its valve closing position solely under the influence of gravity. In the case of small ventilating valves, for instance valves having an outer diameter in the order of 13-50 mm, the fact that the valve body is light in weight means that the gravitationally effected closing force becomes too weak. Another drawback is that the valve-member sealing element, a rubber plate or washer, cannot be made soft or pliable at a free-supporting rim part to compensate for the small closing force, because the one outer free-supporting rim part of the washer is then able to snap passed its sealing ridge already at relatively low over-pressures in the conduit relative to the surrounding atmosphere. It is not appropriate to increase the weight of the valve member, because of inertia.
Consequently, it has been preferred in practice to also fit a spring in the valve to supplement the effect of the gravitational force in achieving desired sealing/valve-closing conditions, particularly in the case of small valves. Although the spring ensures an effective sealing action, it adds to the magnitude of the pressure difference required to open the valve.